1. Field of the Invention
This invention generally relates to a bicycle rear derailleur. More specifically, the present invention relates to a bicycle rear derailleur that uses three pulleys to guide and tension a bicycle chain.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle rear derailleur.
A rear derailleur typically has a main derailleur body and a chain guide or cage 13 with a first or guide pulley and a second or tension pulley. The main derailleur body basically has a base member, a linkage or moving mechanism and a movable member. The base member is typically a stationary member that can be mounted to the rear part of the bicycle frame. The linkage or moving mechanism has one end that is mounted to the base member and the other end mounted to the moving mechanism. The movable member is capable of relative movement with respect to the base-member between a top gear position and a low gear position. The chain guide is pivotally mounted to movable member. A biasing member is typically provided to bias the movable member in one direction relative to the base member. The biasing member is a coil spring, for example, that is mounted inside the link mechanism. In order to maintain appropriate tension a bicycle chain, the movable member typically includes a spring that biases the chain guide to a retracted position. The chain guide often pivotally supports the guide (first) pulley and the tension (second) pulley that is spaced apart from the guide (first) pulley. When tensioned, the chain wraps around the chain pulleys along a serpentine path. The chain guide is configured to move the chain between a plurality of differing diameter chain sprockets in a sprocket set. Since the chain sprockets have differing diameters, the distance between the chain pulleys must be sufficiently large to accommodate the various diameters of the chain sprockets. This requires a corresponding increase in the length of the chain guide. Unfortunately, such an increase in the length of the chain guide is an undesirable design feature in current bicycle configurations. Therefore, it is desirable to reduce the length of the chain guide.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle rear derailleur. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.